A radio frequency (RF) power amplifier is a type of electronic amplifier used to convert a low-power radio frequency signal into a signal of significant power. RF power amplifiers are used to transmit RF signals between mobile devices and base stations located at far distances (e.g., greater than one mile). The efficiency of RF power amplifiers is an important factor of battery life in the mobile devices and power consumption (cost) in RF base stations. An envelope-tracking RF power amplifier allows for high RF power amplifier efficiencies to be achieved. Using envelope tracking, efficiency can be improved by causing the direct current (DC) power supply voltage of the power amplifier to be continuously adjusted and track the envelope of the RF input signal of the amplifier. By having the power supply voltage of the power amplifier track the envelope of the RF input signal, the amplifier can be maintained at or near a saturation point during operation, which is typically the most efficient region of operation.
These and other features of the present embodiments will be understood better by reading the following detailed description, taken together with the figures herein described. In the drawings, each identical or nearly identical component that is illustrated in various figures may be represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. Furthermore, as will be appreciated, the figures are not necessarily drawn to scale or intended to limit the described embodiments to the specific configurations shown. For instance, while some figures generally indicate straight lines, right angles, and smooth surfaces, an actual implementation of the disclosed techniques may have less than perfect straight lines and right angles, and some features may have surface topography or otherwise be non-smooth, given real-world limitations of fabrication processes. In short, the figures are provided merely to show example structures.